Published: September 18, 2026.
Intermodal and drayage carriers do not just move freight. They borrow equipment, and borrowed equipment has a clock. A container or trailer pulled from a terminal or rail ramp is usually allowed a set number of free days. After that, per diem charges accrue until the unit is returned. A missed return date can turn a profitable move into a loss faster than any fuel swing.
Record the interchange as a controlled event
Every interchange is a handoff with a date, a time, a location, and condition. Capture the equipment number, the interchange receipt, the out date, the agreed free days, and the per diem rate. Link the receipt image. Do not rely on a driver's memory of when the unit was picked up.
The same discipline applies at return. Record the return date and time, the receiving location, and the receipt. If the return is rejected because of damage or a missed appointment, record that as a separate event with its own evidence. A rejected return usually keeps the clock running, which is exactly when a carrier needs clear documentation.
Put free-day expiration on a calendar
The tracker's most important output is a date: when free time ends. Put that date on a shared calendar with the unit number and the load. Give someone the job of checking the calendar every day and flagging units approaching their last free day.
Warnings should come with enough lead time to act. A warning the morning free time expires is too late to schedule a return or a swap. Many carriers set alerts at two days and one day before expiration, plus an escalation on the last free day if nothing is scheduled.
Reconcile per diem invoices line by line
The per diem invoice is where errors hide. Reconcile each charge against the tracker: equipment number, out date, in date, free days, rate, and any agreed exceptions. Flag lines where the out date differs from the interchange receipt, where free days are shorter than the agreement, or where a unit appears twice.
Keep the disputed amount separate from the accepted amount so the carrier does not stall payment on the whole invoice. A clear dispute letter with the receipts attached gives the billing party a reason to correct the charge quickly.
Handle detention and appointment delays
Much per diem exposure comes from delays outside the carrier's control: a terminal that will not accept a return, a shipper that holds the unit, a rail ramp with a long queue. These events should be logged with times and, where possible, names and confirmation numbers.
The tracker should show why a unit stayed out longer than planned and what evidence supports the reason. When a customer or facility caused the delay, the carrier's owner can decide whether to seek reimbursement. The office's role is to make the sequence provable, not to argue the charge with the terminal.
Keep equipment condition records sharp
Interchange is also where damage disputes begin. Photos taken at pickup and return, with timestamps, protect the carrier from being charged for damage it did not cause. Note the condition of tires, lights, doors, and the undercarriage, and record any pre-existing damage on the interchange receipt.
If the carrier is charged for damage, attach the pickup photos and the receipt to the dispute. A short chronology with dated images is far more persuasive than a phone call made weeks later.
Coordinate with dispatch and yard
The tracker only works if dispatch knows a unit is about to accrue charges. Build a daily handoff that tells dispatch which units are due, which returns are scheduled, and which units are stuck. That lets dispatch plan the next move around the return instead of discovering the problem after the invoice arrives.
The yard should also see the list, because a return often depends on the yard's capacity to receive the unit.
Close the month with a cost report
Summarize per diem by customer, by terminal, and by reason. This report tells the carrier where accessorial costs are coming from and which customers or facilities are consistently the source. Over time, that data supports better pricing and better decisions about which lanes or terminals to avoid.
The report also reveals process gaps. If returns are frequently late because the office learns about free-day expiration too late, adjust the alert schedule rather than blaming the driver.
Questions teams usually ask
Who owns free days and per diem rates?
They come from the interchange agreement between the carrier and the equipment provider. The office should keep a current copy or reference and use it when reconciling invoices.
What if the terminal refuses a return?
Record the attempt, the location, the time, who was spoken to, and any reference number. That evidence supports a dispute or a request to pause the clock. Then escalate to the provider through the carrier's approved contact.
Is per diem the same as detention?
No. Detention is usually a customer charge for holding a truck beyond an appointment. Per diem is an equipment charge from the equipment provider for keeping a unit beyond free days. They are tracked differently and billed to different parties.
How can the office reduce exposure?
Earlier alerts, a daily return plan, and quick documentation of facility-caused delays. Most per diem surprises come from late information, not from long free periods.
A per diem tracker is a cost-control tool disguised as a paperwork routine. When out dates, free days, and returns are visible every day, accessorial charges stop arriving as surprises and start behaving like numbers a carrier can manage.
Want help keeping interchange dates and per diem charges under control? Contact our team to learn how a trucking virtual assistant can run the tracker.